How to use something like `std::basic_istream<std::byte>`

Question

This question aims for using std::byte with standard input-output.

Are there any plans to add proper function overloads for read(_bytes) and write(_bytes) to the interfaces of basic_istream<CharT> and basic_ostream<CharT> in a future standard? What reasons speak against it? I understand that the CharT* -overloads should be kept. What can I do to use std::byte ? I currently define in my project functions

std::istream& read(std::istream&, std::byte*, std::streamsize)
std::ostream& write(std::ostream&, const std::byte*, std::streamsize)

These use reinterpret_cast<> to char* resp. const char* but I believe this depends on the size of char . Am I wrong? Is char always 1 byte ?

I tried to make std::basic_istream<std::byte> but it is missing std::char_traits<std::byte> and so on. Did anyone make this kind of thing work already?

Answer 1

Don't.

Whether you're operating in "text mode" or "binary mode", what you are still doing fundamentally is acting on characters .

std::byte is not for this purpose, and that's why it does not have these features. Indeed, it was deliberately introduced not to have them!

enum class byte: unsigned char {}; (since C++17)

std::byte is a distinct type that implements the concept of byte as specified in the C++ language definition.

Like char and unsigned char , it can be used to access raw memory occupied by other objects ( object representation ), but unlike those types, it is not a character type and is not an arithmetic type. A byte is only a collection of bits, and only bitwise logic operators are defined for it.

^{http://en.cppreference.com/w/cpp/types/byte}

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Did anyone make this kind of thing work already?

No, everyone deliberately didn't, as explored above.

Use char or unsigned char , as we have done for decades!

Answer 2

P2146: Modern std::byte stream IO for C++ is a proposal related to your request. The status is tracked on Github .